Light source apparatus and measurement method

ABSTRACT

An acousto-optic tunable filter  4  including: an acousto-optic crystal  41 ; an acoustic wave driver  42 ; and a piezoelectric transducer  43 , is provided in front of a light source section  2  including a plurality of light sources  2 A,  2 B, . . .  2 N having different wavelength characteristics. The frequency of RF generated by the acoustic wave driver  42  is varied in accordance with a desired wavelength. Thus, the light having the desired wavelength is incident on a converging lens  5  as plus and minus first-order light beams, and the light having wavelengths other than the desired wavelength is incident on a converging lens  5  as a zero-order light beam. The converging lens  5  converges the plus and minus first-order light beams and the zero-order light beams at positions different from each other. A selector  6  having openings located at the positions onto which the plus and first-order light beams are converged is provided in front of the converging lens  5 . Therefore, only the light having the desired wavelength can pass through the selector  6  and is emitted from the light source apparatus  1.

TECHNICAL FIELD

The present invention relates to a light source apparatus for selectingor separating light having a required wavelength from light emitted froma single light source or a plurality of light sources and projecting thelight. More particularly, the present invention relates to a lightsource apparatus used for obtaining information of a measured objectbased on the intensity of transmitted light or reflected light(including scattered light) obtained by irradiating the measured objectwith visible light or near-infrared light.

BACKGROUND ART

In recent years, various kinds of optical measurements have beenperformed using light transmitted through, reflected by, or scatteredby, a measured object. In performing such an optical measurement, theintensity of transmitted light, reflected light, or scattered light,obtained by irradiating a measured object with light is detected,thereby obtaining information of the measured object.

Light having a preferred wavelength suitable for the measured object isselected as the light used for the measurement. On the other hand, evenwhen the measurement is performed with respect to the same measuredobject, the intensity of the resulting transmitted light, reflectedlight, or scattered light, differs depending upon the wavelengthselected for the measurement. Thus, a preferred wavelength must beselected in consideration of the measurement conditions. In order torealize highly sensitive measurement, it is necessary to project lightincluding a light beam having the wavelength thus selected onto themeasured object with high precision.

In performing such an optical measurement, a light source apparatusincluding a combination of at least one light source emitting lighthaving a plurality of wavelengths and a plurality of filters havingrespectively different transmission wavelengths has conventionally beenused. In such a conventional light source apparatus, a plurality offilters are movably provided. Depending on a wavelength used formeasurement, one of the plurality of filters is selected and then movedto a position suitable for receiving a light emitted from the lightsource, including light with the required wavelength, thereby projectingthe light beam with the wavelength used for measurement onto a measuredobject.

However, in such a conventional light source apparatus, in order tosequentially change the wavelengths of the light beams to be incidentonto the same measured object (i.e., in order to perform a scanning ofthe wavelengths), the plurality of filters are required to besequentially interchanged by mechanically moving a filter unit. Thus,such a conventional apparatus has a problem in that the configurationand the operation of the entire apparatus becomes complicated or thesize thereof becomes large.

In addition, in a conventional light source apparatus, the quantity oflight adversely becomes unstable depending upon the ambient temperaturearound the light source. Moreover, in the case where such a light sourceapparatus includes a plurality of light sources, every time a lightsource emitting light with the wavelength used for measurement isselected from the plurality of light sources, the power supplies of thelight source are required to be turned ON/OFF. Thus, every time lightsources are switched, it takes a significant period of time until thequantity of light is stabilized. Furthermore, since the light sourcesthemselves have respectively different wavelength characteristics and aplurality of filters are used, the intensity of light emitted from theconventional light source apparatus varies depending on the wavelengththereof.

Furthermore, light which has been incident on the measured object andthen transmitted through, reflected by or scattered by the measuredobject is used for performing the above-described optical measurement.Thus, the intensity of the light used for measurement is affected by theabsorption of light by the measured object.

An exemplary relationship between the intensity I₀(λ) of the lightirradiated onto the measured object and the intensity I(λ) of the lighttransmitted through the measured object is shown in FIG. 7. As shown inFIG. 7, because the light has been absorbed by the measured object, thelight intensity greatly differs between the incident light and the lightused for measurement (in this case, the transmitted light). Therefore,in order to maximize the measurement resolution, the sensitivity of alight-receiving system is required to be varied in accordance with theintensity of the light used for measurement.

The present invention has been made in view of the above-mentionedcircumstances and has objectives of providing a stable light sourceapparatus which can project a light beam having a wavelength requiredfor measurement onto a measured object with high precision and also caneliminate the variation in the emission intensities with respect to thewavelengths, and providing a light source apparatus which can beoperated easily and can be downsized.

DISCLOSURE OF INVENTION

The light source apparatus of this invention includes a light sourcesection for emitting light having a plurality of wavelengths and afilter for selecting light having a single wavelength from the lighthaving the plurality of wavelengths, and for separately outputting lighthaving the selected wavelength, the selected wavelength beingelectrically variable, thereby realizing the above objectives.

An intensity of the light having the selected wavelength may beelectrically variable.

The filter may be an acousto-optic tunable filter.

The filter may output the light having the selected wavelength in adirection different from directions in which remaining light havingother wavelengths is output.

The filter may output the light having the selected wavelength as plusand minus first-order light beams and the remaining light as azero-order light beam.

The light source apparatus may further include a combining member forcombining the plus and minus first-order light beams into a single lightbeam.

The filter may output the light having the selected wavelength as ±morder light beams and the remaining light as a zero-order light beam,where m is an integer larger than 2.

The light source apparatus may further include a combining member forcombining ±m order light beams into a single light beam.

The light source section may include a plurality of light sources.

The light source section may include a single light source.

The light source apparatus may further include a converging member forconverging the light output from the filter.

The light source apparatus may further include a member for allowing thelight having the selected wavelength to pass therethrough and blockingthe other light.

The filter may be electrically adjusted such that the selectedwavelength is sequentially varied while an intensity of the light havingthe selected wavelength is constant.

The filter may be electrically adjusted such that an intensity of thelight having the selected wavelength is sequentially varied while theselected wavelength is constant.

The light source section may include laser diodes.

The light source section may include light-emitting diodes.

The plurality of light sources may emit a plurality of light beamshaving respectively different wavelength ranges.

The plurality of light sources may be arranged in an array.

The light source apparatus may further include a lens array which isprovided between the light source section and the filter and has aplurality of lenses.

The measurement method of the invention uses light emitted from a lightsource apparatus which includes: a light source section for emittinglight having a plurality of wavelengths; and a filter for selectinglight having a single wavelength from the light having the plurality ofwavelengths, and for separately outputting light having the selectedwavelength, the selected wavelength being electrically variable. Themethod includes the steps of: irradiating a measured object with thelight emitted from the light source apparatus; receiving lighttransmitted through, reflected by, or scattered, by the measured object;and performing a measurement with respect to the measured object basedon the received light. In the irradiation step, at least one of theselected wavelength and an intensity of the light having the selectedwavelength is sequentially varied, thereby realizing the aboveobjectives.

Another measurement method of the invention uses light emitted from alight source apparatus which includes: a light source section foremitting light having a plurality of wavelengths; and a filter forselecting light having a single wavelength from the light having theplurality of wavelengths, and for separately outputting light having theselected wavelength, the selected wavelength being electricallyvariable. The method includes the steps of: irradiating a measuredobject with the light emitted from the light source apparatus; receivinglight transmitted through, reflected by, or scattered by, the measuredobject as light for measurement; and performing a measurement withrespect to the measured object based on the light for measurement. Themethod further includes a step of electrically adjusting the filter suchthat an intensity of the light for measurement becomes substantiallyconstant without depending upon the selected wavelength, prior to theirradiation step, thereby realizing the above objectives.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of a filter used in the light sourceapparatus according to the present invention.

FIG. 2 is a cross-sectional view schematically showing the configurationof the light source apparatus according to the present invention.

FIG. 3 is a figure illustrating an example of the wavelengthcharacteristics of a light source section of the light source apparatusshown in FIG. 2.

FIG. 4 is a figure illustrating an example of the wavelengthcharacteristics of a light beam emitted from the light source apparatusshown in FIG. 2 when the light source section has the wavelengthcharacteristics illustrated in FIG. 3.

FIG. 5 is a figure illustrating another example of the wavelengthcharacteristics of a light beam emitted from the light source apparatusshown in FIG. 2 when the light source section has the wavelengthcharacteristics illustrated in FIG. 3.

FIG. 6 is a figure illustrating still another example of the wavelengthcharacteristics of a light beam emitted from the light source apparatusshown in FIG. 2 when the light source section has the wavelengthcharacteristics illustrated in FIG. 3.

FIG. 7 is a figure illustrating exemplary wavelength characteristics ofthe light emitted from a conventional light source apparatus and thelight for measurement obtained by irradiating a measured object with theemitted light.

FIG. 8 is a figure illustrating the process steps for adjusting theintensities of the light beams emitted from the light source apparatusshown in FIG. 2 in performing an optical measurement using the lightsource apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the light source apparatus according tothe present invention will be described with reference to theaccompanying drawings.

FIG. 1 illustrates a filter used for selectively outputting light havinga single wavelength from light having a plurality of wavelengths in thelight source apparatus according to the present invention. The filter isformed of an acousto-optic tunable filter (AOTF) which is a band passfilter for electrically scanning a wavelength. The acousto-optic tunablefilter 4 includes: an acousto-optic crystal 41; an acoustic wave driver42; a piezoelectric transducer 43; and an absorber 44. The acousto-optictunable filter 4 receives incident light including a plurality ofwavelength components and then selectively outputs light containing asingle wavelength component and components in the vicinity of the singlewavelength. The acousto-optic tunable filter 4 used in the light sourceapparatus according to the present invention is of a “non-collinear”type in which the propagation direction of the acoustic wave applied tothe acousto-optic crystal 41 crosses the propagation direction of thelight in the acousto-optic crystal 41. The acousto-optic crystal 41herein is made of tellurium dioxide (TeO₂). The wavelength to beselected can be changed by varying the frequency of the RF signalsupplied to the piezoelectric transducer 43 from the acoustic wavedriver 42. Therefore, it is no longer necessary to provide a mechanicalmovable portion which has conventionally been necessary for moving thefilters. In addition, it is not necessary to repeat the opticalcalibrations.

Hereinafter, the operation of the acousto-optic tunable filter 4 will bedescribed with reference to FIG. 1.

When an RF signal generated by the acoustic wave driver 42 is suppliedto the transducer 43, the RF signal is converted by the transducer 43into an acoustic wave to be applied to the acousto-optic crystal 41. Inthe acousto-optic crystal 41, when the acoustic wave passestherethrough, a distortion is caused in the crystal lattice. Thisdistortion of the crystal lattice functions as a grating for lighthaving a single wavelength. Thus, the acousto-optic crystal 41 under theapplication of an acoustic wave selectively diffracts the light havingthe single wavelength and then outputs the light as plus and minusfirst-order diffracted light beams. That is, the angle of diffractiondepends on the frequency of the acoustic wave applied to theacousto-optic crystal 41. Light having wavelengths other than the singlewavelength transmitted through the acousto-optic crystal 41 outgoes as azero-order diffracted light beam, toward a direction different from thedirections of the plus and minus first-order diffracted light beams.Thus, light having a wavelength selected by the filter is separated fromthe remaining light having wavelengths other than the selectedwavelength.

The wavelength of the light which is selectively diffracted by theacousto-optic crystal 41 is determined in accordance with the frequencyof the acoustic wave. Therefore, the wavelength to be selected can bevaried by varying the frequency of the RF signal generated by theacoustic wave driver 42. In addition, in the acousto-optic tunablefilter, the intensity of the light outgoing from the acousto-opticcrystal 41, i.e., the intensity of the diffracted light, is determineddepending upon the power of the RF signal generated by the acoustic wavedriver 42. Thus, if the power of the RF signal is adjusted, light havinga desired intensity (quantity of light) can be obtained. As describedabove, since the light source apparatus according to the presentinvention uses an acousto-optic tunable filter 4, it is possible toelectrically change the wavelength and the intensity (quantity) of lightselected by the filter.

Next, the configuration of the light source apparatus according to thepresent invention will be described with reference to FIG. 2.

FIG. 2 is a cross-sectional view schematically showing the configurationof the light source apparatus according to the present invention.

The light source apparatus 1 includes a light source section 2; a lensarray 3; an acousto-optic tunable filter 4; a converging lens 5; aselector 6; and a combining element 7. The light source section 2 isconfigured so as to emit a plurality of light beams having a pluralityof wavelength ranges. In this embodiment, a light source array includinga plurality of light sources 2A, 2B, 2C, . . . 2N, which emit lightbeams having respectively different wavelengths, is used as the lightsource section 2. Preferably, a plurality of light sources having anequal output intensity are used as the light sources 2A, 2B, 2C, . . .2N. The power supplies of these light sources are not required to beturned ON/OFF discontinuously as is done in a light source of aconventional light source apparatus. The reason is as follows: Since thewavelength to be separated is selected only by electrically adjustingthe acousto-optic tunable filter 4, it is no longer necessary to selecta light source in accordance with the wavelength to be selected as isdone in a conventional light source apparatus. Laser diodes,light-emitting diodes or the like can be used as the plurality of lightsources. Also, these light sources may be arranged either inone-dimension or two-dimension. Alternatively, a plurality of lightsources may be arranged in a circular arrangement.

Instead of using a plurality of light sources, a single light source(e.g., a fluorescent lamp) which has broad wavelength characteristics orcan emit light having various wavelengths may be used. Whether aplurality of light sources are used or a single light source is used,the power supply of each light source must be activated beforehand.Thus, the light source(s) can only be used in a state where the outputof the power supply is stabilized and the quantity of light emitted fromthe light source is stable.

The lens array 3 is provided in front of the light source section 2. Thelens array 3 collimates the plurality of light beams having a pluralityof wavelengths which have been emitted from the light source section 2into collimated light beams and then directs the collimated light beamsbe incident onto the acousto-optic tunable filter 4. In this embodiment,the lens array 3 includes the same number of converging lenses 3A, 3B,3C, . . . 3N as the number of light sources constituting the lightsource array.

The light beams collimated by the lens array 3 are incident onto theacousto-optic tunable filter 4. The acousto-optic tunable filter 4selectively diffracts light beams having a desired wavelength to directthe diffracted light beams as plus and minus first-order diffractedlight beams toward directions different from the direction toward whichlight beams having wavelengths other than the desired wavelength isdirected as a zero-order diffracted light beam, as described above.Thus, the acousto-optic tunable filter 4 outputs the plus and minusfirst-order light beams and the zero-order light beams in respectivelydifferent directions. The converging lens 5 receives the light beamsoutput from the acousto-optic tunable filter 4 and then converges theplus and minus first-order light beams and the zero-order light beams atthe respective positions corresponding to the incidence directionsthereof. Accordingly, only the light having a desired wavelength isconverged onto the positions different from the position onto which thelight having other wavelengths is converged.

A selector 6 having two openings is provided in front of the converginglens 5. The selector 6 is disposed such that these two openings arelocated at the positions onto which the plus and minus first-order lightbeams are converged. Therefore, the light beams other than the lightbeams having a desired wavelength are blocked by the selector 6, so thatthe measured object is irradiated only with the plus and minusfirst-order light beams through the openings.

A combining element 7 is disposed in front of the selector 6. Thecombining element 7 combines the plus and minus first-order light beamswhich have passed through the openings of the selector 6 into a singlelight beam. In this embodiment, a multi-branch fiber having two inputsections and one output section is used as the combining element 7.However, the combining element 7 is not limited to a multi-branch fiber.Alternatively, any arbitrary element can be used so long as the elementcan combine the plus and minus first-order light beams incident from twodirections into one light beam to be output. For example, a light guideor the like can be used.

In this way, the light source apparatus 1 according to the presentinvention can separate light having a desired wavelength from lighthaving a plurality of wavelengths merely by performing an electricaladjustment and then can emit the light at a desired intensity.

An example of the wavelength characteristics of the light source section2 is illustrated in FIG. 3. In this example, the light source section 2emits light beams having three different wavelengths of 1065 nm, 1153 nmand 1287 nm. In this embodiment, an array in which three laser diodesare arranged is used as the light source section 2. In this case, if thefrequency of the acoustic wave driver 42 is set to be 90.665 MHz, then alight beam having a wavelength of 1065 nm can be selected as shown inFIG. 4. On the other hand, if the frequency of the acoustic wave driver42 is set to be 83.746 MHz, then a light beam having a wavelength of1153 nm can be selected as shown in FIG. 5. Furthermore, if thefrequency of the acoustic wave driver 42 is set to be 75.260 MHz, then alight beam having a wavelength of 1287 nm can be selected as shown inFIG. 6. Thus, the light source apparatus according to the presentinvention can change the wavelength to be selected by the acousto-optictunable filter 4 by varying the frequency of an electric signal suppliedfrom the acoustic wave driver 42 to the transducer 43.

As described above, in the light source apparatus according to thepresent invention, the wavelength of the light emitted from the lightsource apparatus can be electrically adjusted. Therefore, if the lightsource apparatus according to the present invention is used, then it ispossible to efficiently perform, for example, an optical measurement inwhich the wavelengths of the light to be incident on the same measuredobject are sequentially varied, a so-called “wavelength scanning”. Inaddition, since it is possible to electrically adjust the wavelengths ofthe light emitted from the light source apparatus and also theintensities (or the quantity) of the light, it is also possible toefficiently perform an optical measurement in which the intensities ofthe light beams to be incident on the measured object are sequentiallyvaried.

As described above, in the case of using a conventional light sourceapparatus, in order to sequentially vary the wavelengths of the light tobe incident on one measured object, the operation and the mechanism ofthe light source apparatus become adversely complicated. Moreover, asshown in FIG. 7, even when the same measured object is measured, theintensities of the transmitted light, the reflected light or thescattered light obtained as the light for measurement are greatly varieddepending upon the wavelengths of the light for irradiation. Thus, whena wavelength scanning is performed with respect to a measured object, itis necessary to vary not only the wavelengths but also the sensitivitiesof a light-receiving system for receiving the light for measurement.

On the other hand, if the light source apparatus according to thepresent invention is used, then such an optical measurement in which thewavelengths of the light incident on one measured object aresequentially varied can be performed in the following manner. First,light having arbitrary wavelength-intensity characteristics is emittedfrom the light source apparatus so as to be incident on a measuredobject. In this embodiment, the object is irradiated with light l₀(λ)having wavelength characteristics represented by the broken line in FIG.8. Next, based on the wavelength characteristics of the light obtainedby this measurement, the incident light having such wavelengthcharacteristics (the light intensity at each wavelength) as making theintensities of the light for measurement substantially constant withrespect to each wavelength is determined. In this embodiment, theincident light I₀′(λ) having wavelength characteristics represented bythe one-dot chain in FIG. 8 is selected as the incident light which canmake the intensities of the light for measurement substantially constantwith respect to each wavelength.

Then, while adjusting the power of the acoustic wave driver 42 of theacousto-optic tunable filter 4 so that the wavelengths of the lightselected by the acousto-optic filter 4 are sequentially changed. In thisway, light for measurement I′(λ) having substantially flat wavelengthcharacteristics can be obtained.

As described above, if the light source apparatus according to thepresent invention is used, it is possible not only to easily perform anelectrical scanning of the wavelengths with respect to the same measuredobject, but also make the intensity of the light for measurementobtained by the wavelength scanning substantially constant. Therefore,it is no longer necessary to vary the sensitivity of a light-receivingsystem used for the measurement in accordance with the wavelengths. Inaddition, it is also possible to set the measurement area of alight-receiving system to be narrow. Alternatively, in electricallyadjusting the intensity of the light emitted from the light sourceapparatus, it is also possible to adjust the power of the acoustic wavedriver of the acousto-optic tunable filter in accordance with themeasurement area of the light-receiving system.

In the above described embodiment, an array of a plurality of lightsources is assumed to be used as the light source section 2.Alternatively, the light sources may be arranged as a one-dimensionalarray or a two-dimensional array or in a circular arrangement.

Also, in the above-described embodiment, a lens array 3 is used fordirecting the light emitted from the light source section 2 be incidentonto the acousto-optic tunable filter 4. However, even in the case ofusing a multi-branch fiber having a plurality of light inputsrespectively corresponding to the plurality of light sources and onelight output, instead of the lens array 3, for example, the lightemitted from the light source section 2 can be efficiently convergedonto the acousto-optic tunable filter 4.

In the above embodiment, an example in which light having a selectedwavelength is separated as plus and minus first-order diffracted lightbeams, has been described. However, the present invention is not limitedthereto, the light having a selected wavelength may be separated ashigher order diffracted light beams (±m order light beams, m is aninteger larger than 2).

INDUSTRIAL APPLICABILITY

As is apparent from the foregoing description, the light sourceapparatus according to the present invention selects light having asingle wavelength from light having a plurality of wavelengths and thenoutputs the selected light beam separately from the remaining lightbeams having other wavelengths. The wavelength to be selected can bechanged by electrically varying the set values of the filter. Morespecifically, the wavelength of light to be separated can be changed byvarying the frequency of the RF signal generated by the acoustic wavedriver of the acousto-optic filter used as a filter. Therefore, it is nolonger necessary to provide a plurality of filters so as to correspondto the respective wavelengths and interchange the filters in accordancewith the wavelength to be selected, so that the configuration and theoperation of the light source apparatus can be simplified and the sizeof the entire light source apparatus can be reduced. In addition, lighthaving a desired wavelength can be obtained with high precision.

Moreover, the light source apparatus according to the present inventioncan electrically vary the wavelength to be selected by the filter andalso the intensity of the light beam to be selected by and output fromthe filter. Specifically, by varying the RF power of the acoustic wavedriver of the acousto-optic tunable filter used as the filter of theinvention, the intensity of the light output from the acousto-optictunable filter can be varied.

Furthermore, in the light source apparatus according to the presentinvention, the wavelength of the light emitted from the light sourceapparatus is electrically selected by the filter. Thus, even when aplurality of light sources are provided, it is no longer necessary toturn ON/OFF the power of the light sources as is done in a conventionalapparatus. Since the light sources can always be set in a light-emissionstate, the variation in the quantity (or the intensity) of the lightemitted from the light source apparatus can be reduced. Moreover, sincethe light having the selected wavelength is separated by the filter fromthe remaining light beams having other wavelengths, it is no longernecessary to separate light into a plurality of light beams having aplurality of wavelengths and then make the light beams be incident ontothe filter. Consequently, the configuration of the light sourceapparatus can be simplified.

Moreover, the light source apparatus according to the present inventioncan converge the light having a selected wavelength even when the lighthas been separated from the remaining light having other wavelengths.

Furthermore, the light source apparatus according to the presentinvention can efficiently converge the light having a plurality ofwavelengths, which have been emitted from the light source section, ontothe filter. If an array in which a plurality of light sources arearranged is used as the light source section and either a lens arraydisposed so as to correspond to the light sources or a multi-branchfiber having a plurality of light inputs corresponding to the lightsources is disposed in front of the light source array, then it ispossible to converge the light emitted from the light source sectiononto the filer more efficiently.

If a plurality of light sources emitting a plurality of light beamshaving respectively different wavelength ranges are used for the lightsource section, then the wavelength range of the light emitted from thelight source apparatus can be enlarged.

What is claimed is:
 1. A light source apparatus comprising: a lightsource section for emitting light having a plurality of wavelengths; afilter for selecting light having a single wavelength from the lighthaving the plurality of wavelengths, and for separately outputting lighthaving the selected wavelength, the selected wavelength beingelectrically variable, wherein the filter outputs the light having theselected wavelength as ±m order light beams and the remaining light as azero-order light beam, where the ±m order light beams are output indirections which are different from a direction in which the zero-orderlight beam is output, and m is an integer equal to or larger than 1; anda combining member for combining the ±m order light beams into a singlelight beam, wherein the light source section comprises a plurality oflight sources.
 2. A light source apparatus comprising: a light sourcesection for emitting light having a plurality of wavelengths; a filterfor selecting light having a single wavelength from the light having theplurality of wavelengths, and for separately outputting light having theselected wavelength, the selected wavelength being electricallyvariable, wherein the filter outputs the light having the selectedwavelength as ±m order light beams and the remaining light as azero-order light beam, where the ±m order light beams are output indirections which are different from a direction in which the zero-orderlight beam is output, and m is an integer equal to or larger than 1; anda combining member for combining the ±m order light beams into a singlelight beam, further comprising a member for allowing the ±m order lightbeams to pass therethrough and blocking the zero-order light beam.
 3. Ameasurement method for performing a measurement with respect to ameasured object using light emitted from a light source apparatus, themethod comprising the steps of: emitting light having a plurality ofwavelengths; passing the emitted light through a lens array; filteringthe emitted and passed light, said filtering step including the steps ofselecting light having a single wavelength from the light having theplurality of wavelengths, and separately outputting light having theselected wavelength in at ±m order light beams, the selected wavelengthbeing electrically variable in said filtering; and combining at leastthe ±m order light beams into a single combined light beam; irradiatingthe measured object with the combined light beam; receiving lighttransmitted through, reflected by, or scattered by, the measured object,as light for measurement; and performing a measurement with respect tothe measured object based on the received light, wherein the filteringstep further comprises a step of electrically adjusting such that anintensity of the light irradiating in said irradiating step formeasurement becomes substantially constant without depending upon theselected wavelength, prior to the irradiation step.
 4. A light sourceapparatus comprising: a light source section that emits light having aplurality of wavelengths; a filter that selects light having a singlewavelength from the light having the plurality of wavelengths, andseparately outputs light having the selected wavelength, wherein thefilter outputs the light having the selected wavelength as ±m orderlight beams and the remaining light as a zero-order light beam, wherethe ±m order light beams are output in directions which are differentfrom a direction in which the zero-order light beam is output, and m isan integer equal to or larger than 1; a lens array, which is providedbetween the light source section and the filter; and a combining memberthat combines the ±m order light beams into a single output light beam;wherein said filter is electrically adjusted such that the intensity ofthe single output light beam is substantially constant at each of theplurality of wavelengths.